How does a geothermal heat pump work?

Heat pumps don’t create heat. They take existing
heat and move it. Anyone with a refrigerator has witnessed the operation of a
heat pump. Refrigerators collect heat from the unit’s interior and move it to
the exterior for cooling purposes. Unlike a refrigerator, a heat pump can
reverse itself. An air-source heat pump, for example, can extract heat from
outdoor air and pump it indoors for heating purposes.

A geothermal heat pump works the same way, except
that its heat source is the warmth of the earth. The process of elevating
low-temperature heat to over 100°F and transferring it indoors involves a cycle
of evaporation, compression, condensation and expansion. A refrigerant is used
as the heat-transfer medium which circulates within the heat pump. The cycle
starts as the cold liquid refrigerant passes through a heat exchanger
(evaporator) and absorbs heat from the low-temperature source (fluid from the
ground loop). The refrigerant evaporates into a gas as heat is absorbed.

The gasseous refrigerant then passes through a
compressor where the refrigerant is pressurized, raising its temperature to
more than 180°F. The hot gas then circulates through a refrigerant-to-air heat
exchanger where heat is removed and pumped into the building at about 100°F.
When it loses the heat, the refrigerant changes back to a liquid. The liquid is
cooled as it passes through an expansion valve and begins the process again. To
work as an air conditioner, the system’s flow is reversed.